OBAMA’S STUNNING FUNDRAISING NUMBERS…. There were ample reasons to believe that the Obama campaign’s fundraising was very good in September. Obama is blanketing airwaves with expensive television ads, and is buying half-hour prime-time blocks on most of the major networks. There was some speculation that Obama may have blown the doors off the old record and raised $100 million in just one month.

No one could have predicted this.

Democratic presidential candidate Barack Obama reports raising more than $150 million in September in an unprecedented eruption of political giving.

The influx of money has helped the Illinois senator expand the field of competitive states and has widened his financial advantage over Republican rival John McCain.

The monthly figure pushed Obama’s total fundraising to $605 million, unseen before in presidential politics.

According to a video posted by Obama campaign manager David Plouffe this morning, the record-shattering numbers were the result of 632,000 new donors, bringing the new total of donors to over 3.1 million. Just remarkable.

The previous record for the best fundraising month any presidential candidate ever had was Obama in August, when he raised $66 million — far less than half what Obama raised in September.

I vaguely recall some grumbling in Democratic circles a couple of months ago, with many wondering whether the Obama campaign’s fundraising would be strong enough to justify opting out of the public financing system.

$150 million in September seems to answer the question.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.